Ocular specimens and sera from 12 patients with onchocerciasis and 10 controls were studied. A mild to moderate chronic inflammatory cellular infiltration was present in the conjunctiva of the onchocerciasis patients. T-lymphocytes were the predominant inflammatory cells with the T-suppressor subset being significantly increased in the onchocerciasis patients when compared to controls. In the onchoceriasis patients, the nonlymphoid cells in the conjunctiva and iris, such as vascular endothelia, pericytes and fibroblasts, showed an increase in expression of class II antigens. The anti-onchocerca Volvulus antibodies in the sera and aqueous humor were significantly highter in the patients compared to the controls. These findings suggest that T-cells are important in the ocular immune response to onchocerca and that expression of class II antigens on nonlymphoid cells and the humoral factors may all play a critical role in ocular onchocerciasis.